There is some rule (or at least there was...not sure if it still exists under the new CBA) having to do with a player being traded before the waiver draft not being able to play with the team that traded him for a year. If I remember correctly, this happened with Dean McAmmond and the Flames/Avs a few years ago.
Does anyone remember the exact details?

McAmmond was with Calgary - in the waiver draft, he was claimed by Colorado. At that point, he was ineligible to play for Calgary at any point for the rest of that year.

At or close to the trade deadline, Calgary signs off on a deal to reacquire McAmmond - then realizes that he's ineligible to play with the Flames for the remainder of the season.

There was a similar rule in effect for RFA's who signed an offer sheet - if his team matched, they couldn't trade the player for one year. It was put into effect after Marty McSorley got an offer sheet from the Blues, the Kings matched it, and traded McSorley to Pittsburgh for Tomas Sandstrom before the start of the regular season - then traded Sandstrom back to Pittsburgh late in the season to get McSorley back. (Explains why the Rangers tried to pluck Joe Sakic circa 1997 with a 3-year, $21 million offer sheet - paying $15 million the 1st year.)